1. Field of the Invention
The invention relates to an apparatus for changing a vehicle speed setting of cruise control.
2. Description of the Related Art
Cruise control controls a vehicle so that it travels at a constant speed that was selected and set by the driver. Japanese Patent Application Publication No. 2004-114988 (JP-A-2004-114988) describes one such constant speed running control apparatus. This apparatus changes the vehicle speed setting in predetermined amounts according to an operation of a lever by the driver. Operating the lever for a longer period of time increases the predetermined amount that the vehicle speed can be changed. For example, the vehicle speed setting increases (or decreases) by 1 km/h every time the lever is operated up (or down) once. When the lever is held up (or down) for an extended period of time, the vehicle speed setting increases (or decreases) by of 5 km/h.
In the foregoing related art, the vehicle speed starts to change only when the driver performs an operation that is reflected in the operating time of the lever. Therefore, despite the fact that the vehicle speed setting needs to change quicker when the vehicle is traveling in a passing lane of an expressway than it does when the vehicle is traveling in a traveling lane, the speed at which the vehicle speed setting changes (hereinafter referred to as the “change speed of the vehicle speed setting”) in response to a lever operation is the same regardless of which lane the vehicle is traveling in, and therefore does not meet the expectations of the driver. Also, if the vehicle speed setting is changed while the driver is looking off (i.e., not paying attention), for example, it would be undesirable for the change speed of the vehicle speed setting to increase in the same manner that it would while the driver is paying attention to the road. That is, despite the fact that the demand related to the change speed of the vehicle speed setting changes depending on the running environment such as the road type and the state of the driver, with the related art, the change speed of the vehicle speed setting in response to a lever operation is always the same regardless of the running environment, and thus is not always suited to the running environment.